Sigma 166715 225265378 2008-07-12T19:51:29Z 67.100.140.210 correct punctuation and capitalization {{otheruses}} {{wiktionarypar3|Σ|σ|ς}} {{Table Greekletters|letter=sigma}} [[Image:Madaba Jerusalem Mosaic.jpg|thumb|200px|The [[Madaba Map]], a sixth-century mosaic map of [[Jerusalem]] ("ΗΑΓΙΑ ПОΛΙΣ") uses the lunate sigma.]] '''Sigma''' (upper case '''Σ''', lower case '''σ''', lower case in word-final position '''ς''') is the eighteenth letter of the [[Greek alphabet]]. In the system of [[Greek numerals]] it has a value of 200. When used at the end of a word, and the word is not all [[upper case]], the final form (ς) is used. (e.g. ''Ὀδυσσεύς'' (Odysseus) - Note the two sigmas in the center of the name, and the word-final sigma at the end.) Not to be confused with the [[cedilla]] [[ç]]. The letter is ultimately derived from [[Phoenician alphabet|Phoenician]] [[Shin (letter)|Šin]] 𐤔. However, its name derives from [[Samekh]]. The uppercase form of sigma was borrowed into the [[Latin alphabet]] to serve as the uppercase of [[esh (letter)|esh]] (lowercase: {{unicode|ʃ}}). == Lunate sigma == In Eastern forms of Greek writing (as opposed to the [[Western Greek alphabet]] used in the European Greek colonies) and in the Middle Ages, the '''lunate sigma''' (upper case {{Unicode|Ϲ}}, lower case {{Unicode|ϲ}}) — which resembles, but which is not at all related to, the [[Latin alphabet|Latin letter]] [[C]] — was often used. Lunate sigma was frequently used for writing [[Medieval Greek]], and it can still sometimes be seen in inscriptions in [[Eastern Orthodox Church|Greek Orthodox churches]], but also in certain printed editions of classical authors. The form of the [[Cyrillic alphabet|Cyrillic letter]] [[Es (Cyrillic)|С]] [s] and [[Coptic alphabet|Coptic letter]] ''sima'' are derived from lunate sigma. On coins from the [[Indo-Greek|Hellenistic period in India]], the script of later coins sometimes use lunate sigma. This sigma continued to be written this way also in [[Medieval Greek]]. A dotted lunate sigma (''sigma periestigmenon'', encoded at U+03FE {{unicode|Ͼ}}) is used by [[Aristarchus of Samothrace]] as an editorial sign indicating that the line so marked is at an incorrect position. Similarly, an [[antisigma]] (encoded at U+03FD {{unicode|Ͻ}}) may mark a line that is out of place. A dotted antisigma (''antisigma periestigmenon'', encoded at U+03FF {{unicode|Ͽ}}) may indicate a line after which rearrangements should be made, or to variant readings of uncertain priority. ==Science and mathematics== Upper case Σ is used as a symbol for: * the [[summation]] operator * a class of [[baryon]]s in [[particle physics]] * macroscopic [[cross section]]s in [[nuclear physics|nuclear]] and [[particle physics]] * in [[economics]] this letter is for the [[balance]] of the invoice classes, the overall amount of the debts and demands * in linguistics and computer science it is used to refer to the set of symbols that form an alphabet Lower case σ is used for: * [[sigma bond]]s in [[chemistry]] * the parametric [[standard deviation]] of a population (as opposed to a sample) in [[statistics]] * a quality model for business, [[Six Sigma]], based on the [[standard deviation]], often referred to as "'''6σ'''" * [[sigma-algebra]]s, sigma-fields and [[Sigma-finite measure|sigma-finiteness]] in [[Measure (mathematics)|measure theory]]; more generally, the symbol ''σ'' serves as a shorthand for "[[countable set|countably]]", e.g. a ''σ''-compact [[topological space]] is one that can be written as a countable [[union (set theory)|union]] of [[compact space|compact subsets]]. * the [[divisor function|sum-of-divisors function]] in [[number theory]] * the [[Stefan-Boltzmann constant]] * the "[[sigma factor]]" of [[RNA polymerase]] * a measure of [[electrical conductivity]] * [[Normal stress|Normal]] [[Stress (physics)|stress]] in [[continuum mechanics]] * volatility of a [[stock]] generally needed for [[options pricing]] * a [[syllable]] in [[phonology]] * the [[spectrum of a matrix]] <math>A</math>, denoted as <math>\sigma(A)</math>, in [[applied mathematics]] * [[surface tension]] * In relational algebra sigma is used to define the unary operation selection on a database relation. ==Politics== During the 1930s, an upper case Σ was in use as the symbol of the [[Brazilian Integralism|Ação Integralista Brasileira]], a radical right-wing party in [[Brazil]]. ==Popular culture and use in fiction== *In a practice similar to [[faux Cyrillic]], capital sigmas are sometimes used in place of Roman [[E]] to give a Greek flavour to titles or text. *Author [[James Rollins]]'s books contain a fictional government agency known as Sigma Force. * [[Mercury-Atlas 8]] was called Sigma 7. *Sigma 2,3,5,6,7,8,9 computers produced by [[Xerox|Xerox Data Systems]] in the 1970s following purchase of SDS, Scientific Data Systems, by it. Successful range of scientific computers similar to IBM 370's. * [http://sigmakee.sourceforge.net Sigma] is the name of a system for [[ontology]] development and reasoning *There is a [[sorority]] named [[Sigma Sigma Sigma]] and the [[Phi Sigma Alpha]] Fraternity goes by the name of [[Phi Sigma Alpha|Sigma]] Fraternity. *There are nine historically black Greek-letter organizations (BGLOs) that make up the National Pan-Hellenic Council. Collectively, these organizations are referred to as The Divine Nine. Members of Phi Beta Sigma are known as SIGMAs as well as members of Sigma Gamma Rho Sorority. * Along with other Greek letters, it is used as a classification of the strength of a PSI technique. * [[Sigma Xi]], The Scientific Research Society, was founded 1886 at [[Cornell University]] as an honor society for scientists and engineers. * Sigma Zeta, the honor society for undergraduate science, math, and computer science founded at Shurtleff College in Alton, Illinois, in the autumn of 1925. ==See also== *[[Antisigma]] *[[Disigma]] *[[Sampi]] [[Category:Greek letters]] [[als:Σ]] [[ar:سيغما (حرف إغريقي)]] [[arc:Σ]] [[br:Sigma (lizherenn)]] [[bg:Сигма]] [[ca:Sigma]] [[cs:Sigma]] [[da:Sigma (bogstav)]] [[de:Sigma]] [[el:Σίγμα]] [[es:Σ]] [[eo:Sigmo]] [[eu:Sigma]] [[fr:Sigma]] [[ga:Sigme]] [[gd:Sigma]] [[gl:Sigma]] [[ko:Σ]] [[hr:Sigma]] [[id:Sigma]] [[is:Sigma]] [[it:Sigma (lettera greca)]] [[he:סיגמא]] [[ka:სიგმა (ასო)]] [[ht:Σ]] [[ku:Sigma]] [[la:Sigma]] [[hu:Szigma]] [[ms:Sigma]] [[nl:Sigma (letter)]] [[ja:Σ]] [[no:Sigma]] [[nn:Sigma]] [[nds:Sigma]] [[pl:Sigma]] [[pt:Σ]] [[ru:Сигма (буква)]] [[simple:Sigma (letter)]] [[sk:Sigma]] [[sl:Sigma]] [[sh:Sigma]] [[fi:Sigma]] [[sv:Sigma]] [[th:ซิกมา]] [[tr:Σ]] [[uk:Сигма (літера)]] [[zh:Σ]]